Fluid-cooled slow-wave structure having alternating longitudinal and transverse extending portions



Sept. 13, 1966 s. lTzKAN 3,273,081

`WAVE STRUCTURE HAVING ALTERNAT NG LONGITUDINAL FLUIDGOOLED SLOW I AND TRANSVERSE EXTENDING PORTIONS 2 Sheets-Sheet 1 Filed May 5l, 1962 rNvENToR. [Rw/v@ frz/AN ZOKFU Sept 13, 1966 l. lTzKAN 3,273,081

FLUID-COOLED SLOW-WAVE STRUCTURE HAVING ALTERNATING LONGITUDINAL AND TBANSVERSE EXTENDING PORTIONS 2 Sheets-Sheet 2 Filed May 3l, 1962 INVENTOR. ff? V//VG [rz/(A /v gaaw H. 27M.

ATTR/VEY United States Patent O 3,273,081 FlLlUllD-CLED SLOW-WAVE STRUCTURE HAV- ING ALTERNATIN G LONGITUDINAL AND TRANSVERSE EXTENDING PRTIONS Irving ltzlian, New York, N.Y., assigner to Sperry Rand Corporation, Great Neck, N .Y., a corporation of Delaware Filed May 31, 1962, Ser. No. 198,997 Claims. (Cl. 333-31) This invention relates t-o fluid-cooled high-power electron beam-electromagnetic wave interaction structures for use in traveling wave tube types of electron discharge devices.

It has been found that in the higher power traveling wave tubes presently being developed, the well known slow wave interaction structures commonly used in lowerpower tubes, such as helices and related structures, are not entire-ly satisfactory. Considerable effort has been expended to develop slow wave interaction structures that exhibit the desired electrical characteristics in the highpower tubes. veloped, but most of these have limi-ted application-s and many of them suffer the disadvantages -that they are relatively complicated to construct and are diliicult to cool. The cooling problem is a primary consideration in the higher-power tubes because both the primary electrons in the electron beam and 4the secondary electrons produced at the collector electrode and at the interaction structure itself have considerable energy and generate a considerable amount of heat when they strike the interaction structure. Additionally, the high electric field strengths of the waves propagating in the tube also significantly contribute to the heating of the structure.

Generally, slow wave interaction structure-s can be divided electrically into two classes, open structures and closed structures. Open stru-ctures guide the electromagnetic waves down both the outside and inside of the structure. Helices, and ring-and-bar circuits are examples of open structures. Because the outside of the circuit in the open structure is essential to the interaction process, it must be spaced from the surrounding envelope and the other exterior metallic portions of the tube. The physical spacing and rigidity of the open-type structures are usually provided by dielectric materials which are poor heat conductors. Therefore, cooling problems are of a primary consideration in high-power tubes using open type interaction structures. `Closed structures, on the other hand, guide the electromagnetic waves down the axis of an enclosed cylindrical interaction structure. The mass of metal in this type of structure provides bo-th a good heat-conducting path and good mechanical rigidity. This reduces the severity of the cooling problems, but the frequency bandwidth and interaction impedance characteristics of these types of structures are less favorable than those of the open structures. Therefore, the open type of slow wave interaction structures are preferred -over the closed structures in view of their superior electrical characteristics, provided that satisfactory means can be found for cooling the open type of structures. The present invent-ion is particularly directed to providing open types of interaction structures that possess good electrical characteristics and may be readily cooled without adversely affecting the electrical characteristics.

'It therefore is an obje-ct of this invention to provide a fluid-cooled interaction structure for use in high-power electron discharge devices.

A further object of this invention is to provide a fluidcooled slow wave propagating structure that is easily fabricated by relatively unskilled labor.

Another object of this invention is t-o provide high- A number of structures have been de 3,273,081 Patented Sept. 13, 1966 power slow wave propagating structures of the type classified as open structures.

It is another object of this invention to provide uidcooled high-power electron beam-electromagnetic wave interaction structures having relatively broad bandwidths, and high interaction impedances.

The invention will be described by referring to the accompanying drawings wherein:

IFIG. l is a schematic illustration of a fluid-cooled ringloaded meander line type of slow wave interaction structure constructed in accordance with the present invention;

FIG. 2 is a simplified illustration of a traveling wave tube amplifier incorporating a slovv wave interaction structure constructed in accordance with the present invention, and

FIGS. 3-5 illustrate other types of fluid-cooled slow wave interaction structures constructed in accordance with the present invention.

The slow wave interaction structures constructed in accordance with the present invention are of the type which have been called ring-line circuits, specific examples being the ring-loaded meander line structure described by I, Itzkan and P. I. Crepeau on page 525, Proceedings of the I RiE., February 1961, and the ring and bar circuit described in U.S. Patent 2,836,758.

Referring now in particular .to FIG. 1, the interaction structure 10 illustrated therein is of the ring-loaded meander line type and is comprised of two uid conduits 11 and 12 of a conductive material, each conduit having sinuous ben-ds of uniform periodicity throughout its length. The axial extending portions 13 and 14 of the two conduits lie substantially in a longitudinally extending plane which passes through the electron beam. 'llhe transversely extending portions 1'5 and 16 of the two conduits 11 and 12 project outwardly and are shaped to conform to the circumference of a circle. The transversely extending portions 11S and 1-6 of the conductive conduits are aligned in parallel transverse planes throughout the length of the structure and form circular crosssectional contigurations in the respective planes. The axially extending portions 13 and 14 of the sinuously bent conduits form conductive connectors which join the successive circular coniigurations at diametrically opposite points thereon. `In assemblying the structure of FIG. 1, the two similar conduits 11 and 12 are merely rotated with respect to each other and are secured together at the necessary regions. Another way of considering the resultant coniiguration of the structure of FIG. 1 is to consider that the two conduits 11 and 12 are placed :adjacent each other with their outwardly projecting portions 15 and 16 aligned in parallel transverse planes, and with the two conduits having a one-half period axial displacement.

As may be seen, `the outwardly projecting portions 15 and 16 simulate rings and the .axial-ly extending portions 13 and 14 simulate meander lines extending throughout the length of the structure. -It has been found that the closer the sinuously bent conduits approximate true parallel-aligned rings and meander lines, the better the electrical performance of the structure.

Fluid conduits 11 and 12 desirably are made of copper or are of copper coated steel tubing. The two conduits 11 and 12 may be either spot-welded or brazed together at the regions where the axially extending porti-ons 13 and 14 and the outwardly projecting portions 15 fand 16 come together.

Another possibility of joining together the two conduits 11 and 12 is to place them adjacent each other, but with a small transverse separation therebetween. Short transverse conductive bars then may be secured to the two conduits to secure them together and to rigidify the structure.

As may be seen at the left end of the structure illustrated in FIG. 1, the conductive conduits 11 and 12 are joined together to make a continuous fiuid path at that end of the structure. At the right end of the structure, each of the conduits 11 and 12 extends axially and passes through the envelope of the tube so that they may be connected to lines of a iiuid system that supplies fluid coolant to the interaction structure so as to maintain its temperature below a maximum temperature limit.

Electrical connectors 21 and 22 are respectively connected to the left and right ends of interaction structure 10 and provide means for coupling electromagnetic waves into and out of the structure.

A simplified schematic illustration of a traveling wave tube incorporating the slow wave structure 10 of FIG. 1 is illustrated in FIG. 2 and is comprised of an electron gun assembly 24, which may be of any conventional design, and a collector electrode 25, which similarly may be of any conventional design. Slow wave interaction structure 10 is disposed coaxially about the electron beam that is established between electron gun 24 and collector 25. A magnetizing coil 26 may be disposed about the envelope 27 in the conventional manner. As may be seen, fluid conduits 11 and 12 are joined to the external fluid system that includes the pump 28 land heat exchanger 29. v

As shown in FIG. 1, the periodicity of the interaction structure is uniform throughout its length. However, the periodicity may be varied, if desired, in accordance with known practices to achieve `desired electrical characteristics in the structure.

In the matter of physically supporting the open type structure illustrated in FIG. 1, for the lower frequency structures wherein the diameters of the fiuid conduits 11 and 12 are relatively large, the structure is self-supporting. In higher frequency tubes in which the conduits 11 and 12 are of considerably smaller size, they may be supported by longitudinally extending dielectric rods as is standard practice in the art.

The important dimensions of the interaction circuit illustrated `in FIG. 1 include the axial spacing p between the circular cross-sectional configurations formed by transversely extending portions and 16, the length L of the meandering sections formed by axially extending portions 13 and 14, the thickness t of the conduit, and the radius a of the cross sectional configuration formed by outwardly projecting portions 15 and 16, In evaluating the performance of the type of interaction structure illustrated in FIG. 1, it is found that as the period p of the structure is decreased the phase velocity of the waves propagating thereon is decreased because the loading effect of the ring-like portions of the circuit is increased. At the same time, both the frequency bandwidth and interaction impedance are decreased. As the lengths L of the axially extending meandering portions 13 and 14 are increased the phase velocity is decreased and the interaction impedance and bandwidth are increased. Increasing the thickness t of the conduits 11 and 12 decreases the phase velocity and increases the bandwidth without appreciably affecting the interaction impedance.

' From this it may be seen that it is desirable to use conduits of as small an outer diameter as possible.

Interaction structures having three or more meander Y lines disposed about the circumference of the circular cross-sectional portions of the structure also -may be constructed in accordance with the present invention. For example, the structure illustrated in FIG. 3 has three meandering lines symmetrically disposed about the ringlike portions of the structure. This structure is comprised of three identically shaped conduits 30, 31 and 32, each of which is sinuously bent throughout its length,

t and is further bent so that each of the transversely ex- ;tending portions 33, 34 and 35 form an arcuate section of substantially so that when joined together they form circular configurations in parallel transverse planes throughout the length of the structure. The axially extending portions which form the meandering lines, portions 38 and 39 of conduit 30, for example, lie in longitudinal extending planes that are disposed .at 120 with respect to each other. It may be seen that the three identically shaped conduits 30, 31 and 32 are angularly disposed at 120 with respect to each other and have their corresponding transversely extending sections joined together to form the fluid-cooled ring-loaded meander line `of FIG. 3. Structures having a greater number of meander lines may be constructed by utilizing a number n of identically shaped conduits, wherein n is equal to the number of desired meander lines, and by forming each of the transversely extending outwardly projecting sections to conform to an arc of a circle having an angular extent substantially equal to 360/n, and by joining together the plurality of bent conduits which are disposed at an angle of 360/ n with respect to each other.

A ring-loaded two wire transmission line type of interaction structure also may be formed in accordance with the principles of this invention. This type of structure is illustrated in FIG. 4 and is comprised of two sinuously bent conduits 41 and 42 that are similar in shape to the sinuously bent conduits 11 and 12 of FIG. 1, with the exception that the axially extending portions 44 and 45 extend substantially parallel to the central axis of the structure rather than being of an arcuate shape as the axially extending portions 13 and 14 are in the structure of FIG. 1.

An interaction structure simulating the ring-and-bar interaction structure also may be readily fabricated in accordance with this invention, as illustrated in FIG. 5. In this structure the two conductive conduits 51 and 52 have outwardly projecting transversely extending portions 53 and 54 that are each shaped in a semicircular bend to form substantially circular cross-sectional configurations in uniformly spaced transverse planes throughout the length of the structure. The axially extending portions 56 and 57 of the two conduits are secured together to form the axially extending bar members that join successive pairs of ring-like configurations at diametrically opposite regions.

All of the structures illustrated in the drawings are readily constructed with the use of relatively simple twisting forms and bending jigs or dies, and may be constructed by relatively unskilled labor from commercially available hollow tubes. Thus, by utilizing the relatively simple procedures and readily available materials, slow wave propagating structures of the open type having the most desirable electrical characteristics may be readily fabricated in a form which permits fiuid cooling without requiring appreciable design and construction effort in the remaining portions of the tube.

While the invention has been described in its preferred embodiments it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. A uid-cooled slow wave propagating structure comprised of a plurality n of tubular conduits of conductive material symmetrically disposed about an axis and each lying substantially entirely within a respective angular sector that extends parallel to said axis, n being an integer,

each of said conduits being comprised of alternately disposed longitudinally-extending and transverselyextending portions that are arranged to form a serpentine-like configuration throughout the length of its respective angular sector,

each transversely-extending portion traversing a given angular extent about said axis and the longitudinallyextending portions at the two ends of a transverse portion lying in respective axially-extending planes that intersect along said axis at an oblique angle,

the n conduits being disposed about said 'axis with the transverse portions located in successive transverse planes in a manner to form successive closed contigurations about said axis.

2. A fluid-cooled slow wave propagating structure comprised of,

a plurality n of tubular conduits of conductive material symmetrically disposed about an axis and each lying substantially entirely within a respective angular sector that extends parallel to said axis, n being an integer,

each of said conduits being comprised of alternately disposed longitudinally-extending and transverselyextending portions,

each transversely-extending portion conforming to a 360/ n arc of a circle and the longitudinally-extending portions at the two ends of a transverse portion lying in respectively longitudinally-extending planes that intersect along said axis at an angle of 360/ n,

the n conduits being disposed about said axis with corresponding transverse portions arranged in successive transverse planes in a manner to form circular configurations.

3. The combination claimed in claim 2 wherein the longitudinally-extending portions of the n conductors are angularly disposed at 360/n with respect to each other between each adjacent pair of said circular configurations.

4. A {luid-cooled slow wave propagating structure cornprising,

a plurality of n uid conduits of electromagnetic wave propagating material disposed about an axis and each extending longitudinally in a respective one of n coextensive angular sectors that extend parallel to said axis, n being an integer,

each conduit being comprised of arcuate portions that 4 extend longitudinally and transversely-extending portions that are disposed intermediate said arcuate portions,

the transverse portions conforming to a 360/1z arc of a circle and the longitudinally-extending arcuate portions at the two ends of each transverse portion lying in respective axially extending planes that intersect along said axis at an angle of 360/ n,

the transverse portions of the conduits being positioned to form circular congurations in successive transverse planes along said -axis and the arcuate portions extending between adjacent circular coniigurations being angularly disposed at 360/1z relative to each other, and

means for passing a fluid coolant through said conduits.

5. A fluid-cooled slow Wave propagating structure comprising,

iirst and second uid and electrical conductors extending parallel to an axis and each lying substantially entirely on a respective side of a longitudinal plane through said axis,

each conductor being comprised of a succession of arcuate sections that extend alternately longitudinally -and transversely,

the transversely extending sections of the two conductors being aligned in successive transverse planes and each being arched approximately 180 about said axis to form a circular configuration in each transverse plane,

the longitudinally-extending sections of the two conductors arching outwardly relative to the axis and the conductors being positioned relative to each other so that respective longitudinally-extending sections of the two conductors extend between adjacent circular conigurations at diametrically opposite regions.

References Cited by the Examiner UNITED STATES PATENTS 5/1958 Marchese 313-32 X lO/l960 Bridsall 3l5-3.6

O HERMAN KARL SAALBACH, Primary Examiner. 

1. A FLUID-COOLED SLOW WAVE PROPAGATING STRUCTURE COMPRISED OF A PLURALITY N OF TUBULAR CONDUITS OF CONDUCTIVE MATERIAL SYMMETRICALLY DISPOSED ABOUT AN AXIS AND EACH LYING SUBSTANTIALLY ENTIRELY WITHIN A RESPECTIVE ANGULAR SECTOR THAT EXTENDS PARALLEL TO SAID AXIS, N BEING AN INTEGER, EACH OF SAID CONDUITS BEING COMPRISED OF ALTERNATELY DISPOSED LONGITUDINALLY-EXTENDING AND TRANSVERSLYEXTENDING PORTIONS THAT ARE ARRANGED TO FORM A SERPENTINE-LIKE CONFIGURATION THROUGHOUT THE LENGTH OF ITS RESPECTIVE ANGULAR SECTOR, EACH TRANSVERSLY-EXTENDING PORTION TRANVERSING A GIVEN ANGULAR EXTENT ABOUT SAID AXIS AND THE LONGITUDINALLYEXTENDING PROTIONS AT THE TWO ENDS OF A TRANSVERSLY PORTION LYING IN RESPECTIVE AXIALLY-EXTENDING PLANES THAT INTERSECT ALONG SAID AXIS AT AN ABLIQUE ANGLE, THE N CONDUITS BEING DISPOSED ABOIUT SAID AXIS WITH THE TRANSVERSE PORTIONS LOCATED IN SUCCESSIVE TRANSVERSE PLANES IN A MANNER TO FORM SUCCESSIVE CLOSED CONFIGURATIONS ABOUT SAID AXIS. 